[Android] Silence flag_changer on missing command-line file.

build/android/pylib/flag_changer.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import logging
 
 from devil.android import device_errors
 
 
 class FlagChanger(object):
@@ skipping 10 matching lines @@
     """Initializes the FlagChanger and records the original arguments.
 
     Args:
       device: A DeviceUtils instance.
       cmdline_file: Path to the command line file on the device.
     """
     self._device = device
     self._cmdline_file = cmdline_file
 
     # Save the original flags.
-    try:
-      self._orig_line = self._device.ReadFile(self._cmdline_file).strip()
-    except device_errors.CommandFailedError:
-      self._orig_line = ''
+    self._orig_line = ''
+    if self._device.PathExists(self._cmdline_file):
+      try:
+        self._orig_line = self._device.ReadFile(self._cmdline_file).strip()
+      except device_errors.CommandFailedError:
+        pass
 
     # Parse out the flags into a list to facilitate adding and removing flags.
     self._current_flags = self._TokenizeFlags(self._orig_line)
 
   def Get(self):
     """Returns list of current flags."""
     return self._current_flags
 
   def Set(self, flags):
     """Replaces all flags on the current command line with the flags given.
@@ skipping 106 matching lines @@
 
     # Tack on the last flag.
     if not current_flag:
       if within_quotations:
         logging.warn('Unterminated quoted argument: ' + line)
     else:
       tokenized_flags.append(current_flag)
 
     # Return everything but the program name.
     return tokenized_flags[1:]